Knock Knock, Who’s There?

Riddle: Billy: Knock knock. Lilly: Who's there? Billy: Cow goes. Lilly: Cow goes who?

Answer: Billy: No they don’t, they go moo, not who!

Source: https://www.riddles.com/9881

Billy: Knock knock. Lilly: Who's there? Billy: Cow goes. Lilly: Cow goes who? — Knock Knock, who’s there? by Ghsub v1.

Riddle: Billy: Knock knock. Lilly: Who's there? Billy: Cow goes. Lilly: Cow goes who? Answer: Billy: No they don’t, they go moo, not who! — by Ghsub v2.